Difference there is a few people in a class vs several thousand baying for your blood, sending you death threats or organising petitions against you.
I do get the point you are making that criticism can be a good tool for improvement, but that depends on both a) the way it is delivered b) if it is valid and c) if you feel it is worth it.
If I was a writer and had the chance to writer, I dunno, Wolverine or the chance to write a solo LGBT star book - I know which is going to sell, I know which is the safer option and I know which is going to stop me from having to be a) the gay writer or b) the gay writer who ruined everything and blah blah blah threads about me sucking online.
Even though I might really feel it needs doing, that doesnt meant I want the argro that comes with it, or frankly, would be strong enough to take it.
It would take the right person, and it's perfectly possible that Marvel haven't had anyone who, when faced with all that, has felt they were the right person at the right time.
In other news, I see the new solicitation are out - As much as I like Kate Bishop, it's beginning to annoy me that the straight white rich girl is the only Young Avenger to get any sort of push. For such a diverse team as it was, in either iteration, it's kinda telling how Marvel still have a long way to go when it comes to crossing some diversity barriers, which ties in to the above.
Maybe they need to get out and find a writer who is strong enough and has a story to tell, similar to how say, a comedy show will go and seek a specific type of comedian to write for them if they have a specific voice they want to use and audience to reach.